Some countries, like Japan, have little or no domestic supply of natural gas. To meet this demand, natural gas produced in Indonesia and/or the Middle East is liquefied and shipped to market in the liquid phase. Upon arrival in Japan, the LNG is offloaded from ships to land based LNG receiving terminals where it is stored in surface tanks in the liquid phase. When users need natural gas, the LNG is vaporized at the receiving terminal and pumped into pipelines for transmission to buyers and sellers. These pipelines vary in length. For example, some electrical generating plants in Japan are built proximate the LNG receiving terminals. Other areas of the world also import LNG, for example, Europe imports LNG from North Africa and elsewhere. The United States also has several LNG receiving terminals that were developed prior to improvements in production of shale gas.
As the LNG is bought and sold, the product needs to be analyzed at each custody transfer point, typically by a gas chromatograph (GC) to determine the Btu content of the product. GC's do not analyze liquids. Price is generally based on the Btu content. Capture of a representative sample and proper analysis is important to buyers and sellers because millions of dollars are exchanged at each custody transfer point.
One early attempt to develop a liquid phase LNG sample collection device is disclosed in U.S. Pat. No. 3,487,692 filed on May 24, 1968 entitled “Method and Apparatus for Sampling Refrigerated Volatile Liquids”. During the 1960's and early 1970's, no single product or procedure received universal approval by both buyers and sellers.
To achieve some standardization in the industry, the International Organization for Standardization (“ISO”) approved three systems for sampling LNG based on a gas phase sample. Standard No. 8943 dated 2007, Mar. 1 has enjoyed wide acceptance on a worldwide level by both buyers and sellers. ISO Standard No. 8943 has been the worldwide benchmark for LNG sampling since it was adopted in 1977.
FIG. 1 of ISO Standard 8943 is a diagram for a first LNG sampling system entitled “Example of continuous sampling for a water-seal-type gas sample holder with a compressor.” This procedure vaporizes the LNG prior to capture in a sample cylinder. This sample cylinder with a gas phase sample is then taken to a laboratory for analysis.
FIG. 2 of ISO 8943 is a diagram for a second LNG sampling system entitled “Example of continuous sampling for a waterless-type gas sample holder”. This procedure also vaporizes the LNG prior to capture in a sample cylinder. This sample cylinder with a gas phase sample is then taken to a laboratory for analysis.
FIG. 3 of ISO 8943 is a diagram for a third LNG sampling system entitled “Example of intermittent sampling for CP/FP sample container.” The CP/FP designation stands for a constant pressure floating piston sample container made by Welker, Inc., assignee of the present application. Like the sample cylinders in FIGS. 1, 2, the CP/FP cylinder also stores a gas phase sample which is then taken to a laboratory for analysis. The Assignee of the present application currently produces sample collection cylinders used in all three systems discussed in this ISO Standard. The present invention is an improvement on the systems described in this ISO Standard.
Unlike the aforementioned prior art which captures the sample in the gas phase, the present invention captures the sample in the liquid phase in a transportable liquid phase LNG sample apparatus (Sample Apparatus). This Sample Apparatus is then taken to a laboratory.
Vaporization of the liquid phase sample may take place at a variety of different locations. For example, vaporization may begin and end during transport from the collection point to the laboratory. In another example, vaporization may begin and end in the laboratory. In yet another example, vaporization may begin during transport and be completed at the laboratory. The liquid phase sample must be allowed to vaporize to the gas phase before analysis because a GC can only analyze gases, as is well known to those skilled in the art. The present invention eliminates substantially all of the equipment in FIGS. 1, 2 and 3 of this ISO Standard, saving money and reducing the chance of leaks and contamination of the sample. Applicant believes that the present sampling apparatus allows both buyers and sellers to capture and transport a more representative sample than any of the prior art listed above.
U.S. patent application Ser. No. 12/234,602 entitled “LNG Sampling Cylinder and Method” filed by the assignee of the present application was an attempt to develop a sample apparatus that could capture a sample in the liquid phase for subsequent delivery to the lab. Unfortunately, the cooling cycle, which must be completed prior to capturing a sample, of this apparatus was lengthy, which delayed field operations. The present invention reduces the length of the cooling cycle and elongates the amount of time available to capture a liquid phase sample.